This invention pertains to mobile storage systems of the type wherein a series of storage units are movable on tracks to create an access aisle between two of the units and to establish the others in close, side by side relationship to thereby minimize the amount of floor space required. In particular, the invention resides in an improved electrical control system that governs automatic positioning of the units in response to a user request and that monitors safety conditions and the integrity of the system in a manner not heretofore achieved.
Some examples of movable storage units are library bookshelves, file cabinets, film storage files and racks used in warehouses and industry to store parts and finished and unfinished goods. Typically, the storage units are mounted on track-guided wheeled carriages each of which has at least one reversible electric motor for propelling it bidirectionally on tracks or rails which may be recessed in the floor. Typically, at least one outermost unit is stationary and the other units are controlled to move toward and away from it to form an aisle.
A desirable control system for effecting sequential movements of units to create an aisle is one wherein there is a motor control module of substantially identical type on each of the movable storage units and the modules are interconnected by conductors that allow cross-communication with each other. Such systems yield the economy that results from being able to manufacture a single type of control. This improves flexibility since the storage units and their control modules can be inserted or removed without requiring modification of other control modules.
Prior art electrical control modules of the type just alluded to are based on the use of relays to obtain the logic functions for controlling unit movement and for monitoring safety conditions. Hence, even though relay-based control modules may be identical in a particular system, if differences are desired in the functional characteristics or features to adapt to the particular requirements of any installation, it becomes necessary to modify, add or substitute hardware components in the control modules and to make changes in the electrical circuitry as well. For instance, it may be necessary to make sure that different safety conditions are met in one installation as compared to other standard installations before any unit will move in response to a user request or will stop if a certain unsafe condition arises. A system that can be modified easily to meet the functional and safety characteristics that may be required by different customers has never been achieved.
One of the problems in existing interconnected individual module control systems is the difficulty of determining the cause of a failure in the system and which module or interconnecting line or line the fault causing the failure has occurred.